Method and apparatus for recompression evaporation



y 59 Pl B. SAbTLER 2,395,546

METHOD AND APPARATUS FOR RECOMPRESSION EVAPORATION Filed Auz. 30, 19 55 2 Sheets-Sheet. l

INVENTOR fhzllipj. Semitic r ZLu MM ATTOR S Jul 21, 1959 P. B. SA'DTLER 2,895,546

METHOD AND APPARATUS FOR RECOMPRESSION EVAPORATION Filed A113. 30, 1955 2 Sheets-Sheet 2 United States Patent (3 METHOD AND APPARATUS FOR RECOM- PRESSION EVAPORATION Philip B. Sadtler, South Norwalk, Conn., assignor to Chicago Bridge & Iron Company, New York, N.Y., a corporation of Illinois Application August 30, 1955, Serial No. 531,564

9 Claims. (Cl. 159-24) This invention relates to compression evaporation and more particularly to a novel method and apparatus for bringing about evaporation by vapor recompression.

Recompression evaporators have been perhaps most extensively used for the purpose of producing distilled water from sea water. In the case of distilled Water production, as well as in certain other applications, the water or liquor fed to the evaporator is at a considerably lower temperature than that at which boiling takes place under conditions of optimum efliciency and economy. In such cases, it is not feasible or practical to boil the water or liquor at as low a temperature as that of the incoming feed liquid, and therefore it has been the practice to pre-heat the feed liquid in countercurrent heat exchangers by bringing it into heat exchange relation with the condensate and/or concentrated liquor from the evaporator. A considerable amount of apparatus and control instrumentation is required to bring about this heat exchange, thus making the evaporator installation somewhat complicated and expensive in terms of both initial cost and maintenance cost.

There are certain industries where the liquids to be evaporated are already at a relatively high temperature and where a condensate of relatively high temperature is desired. For example, in the manufacture of sulfite pulp, large quantities of waste liquor must he economically evaporated so that they can be disposed of in such manner as to avoid contamination of rivers and streams, and such Waste liquors are commonly available for evaporation at a temperature approaching their atmospheric boiling point. Moreover, the condensate from this evaporation process provides a convenient source of wash water for washing the pulp, relatively hot water is more effective for this purpose. Also the concentrated liquor from the evaporator is ordinarily charged to a furnace and hence it too is desirably maintained at a high temperature. Thus for installations of this type it appears desirable to eliminate the heat exchangers previously used. However, the heat content of the recompressed vapor is not sufiicient in itself to both preheat the feed liquor to its boiling point and supply the necessary heat for evaporation, and therefore if the heat exchangers are eliminated additional heat must be supplied from an auxiliary source of heat.

It is accordingly an object of the present invention to provide a recompression evaporation system wherein the step of and apparatus for heat exchanging the feed liquor with the condensate and/or concentrated liquor are eliminated, thereby decreasing both the initial cost and maintenance cost of such an installation. It is another object of the invention to provide a recompression evaporator which delivers high temperature condensate and high temperature concentrated liquor for use in subsequent process operations. It is another object of the invention to provide a recompression evaporator 2 waste liquors. Other objects of the invention in part obvious and in part pointed out hereafter.

In one of its broader aspects, the method of the invention comprises supplying feed liquor to the liquor side of a tubular heating unit of an evaporator for evapo-: ration, compressing the vapors thus evolved and Ciel 1V eringthem to the vapor side of the evaporator heating unit, removing condensate from the vapor side of the heating unit, reducing the pressure on the condensate to cause at least a portion thereof to flash into vapor and compressing the flash vapor and delivering it to the vapor side of the heat exchanger. In this way flash vapor fromthe condensate is used as auxiliary or make-. up steam to maintain the material balance of the cycle upon which the heat balance is dependent and to pro+ vide the additional heat necessary to preheat the feed liquor to its boiling point within the evaporator, and the relatively expensive counter-current heat exchangers previously used can be eliminated.

The many objects and advantages of the present invention can best be understood and appreciated by reference to the accompanying drawings which illustrate apparatus capable of carrying out the method of the invention and incorporating a preferred embodiment and modification of the invention. In the drawings:

Figure 1 illustrates diagrammatically a recompression evaporator having associated therewith a condensate flash chamber according to the present invention and an auxiliary compressor for compressing the condensate flash;

Figure 2 illustrates a modified system wherein the condensate flash is compressed by a steam jet compressor and .a divided heating unit is used to improve the efficiency of operation;

Figure 3 is a horizontal section taken on the line 3-3 of Figure 2 and showing the manner in which the top of the heating unit is divided; and a Figure 4 is a horizontal section taken on the line 44 of Figure 2 and showing the manner in which the bot-' tom of the heatingunit is divided.

Referring to the drawings and particularly to Figure '1, the :compression evaporator there shown comprises an evaporator body 10 and tube-in-shell heating element 12 which are interconnected by pipes 14 and 16 in the usual manner. The hot feed liquor is tntroduced through a pipe 18 to the bottom of heating element 12, flows upwillhe wardly through the tubes thereof wherein it is heated,

that is especially useful in the evaporation of pulpmill thence throughpipe 14 to the evaporator body 10. In the body 10 the evaporated vapors are separated from the concetr-ated liquor which is recirculated through pipe 16 to the bottom of heating element 12. The separated vapors flow to the top of evaporator body 10 and out throughv a vapor pipe 20 to a compressor 22. The pipe 20 contains a conventional vapor drier 21 for vaporizing any entrained moisture in 'the vapors flowing through pipe 20; The vapors are compressed in the compressor 22 and delivered through pipe 24 to the vapor or steam side of the heating element 12 to supply heat to the liquor flowing through the tubes of the heating element. Concentrated liquor is withdrawn from pipe 16 through a pipe26, and condensate is withdrawn from the'steam side of heating element 12 through a pipe 28.

- In accordance with the present invention the conde1isate withdrawn through pipe 28 flows to a flash chamber 30 wherein the pressure on the condensate is reduced to cause a part of it to flash into steam. The condensate flash vapor flows from flash chamber 30 through a pipe Patented July 21,

The flash chamber 30 is .provided with aliquid level regulator 42 to maintain a substantially constant liquid level in the chamber. The condensate leaves the flash chamber through a pipe 44 and flows :to a suitable point of use, such as for example the pulp washers ofa pulp mill.

It will be apparent that in'the system illustrated in Fig ure 1 the countercurrent heat exchangers commonly used with compression evaporators are eliminated. The condensate from heating element 12 is passed through the flash chamber 30 and the pressure in the flash chamber is reduced by the compressor 38 in 'such manner as to cause a portion of the condensate to flash into steam, which is mixed with the main flow of steam from the evaporator body. It is evident that the vapor pressure in the flash chamber 30, which is in communication with the suction of compressor 38, is lower than the pressure inthe compressor discharge pipe-40 and hence lower'than the pressure in vapor'body '10 which is in-comniunication with pipe 40 through pipe 20. By selecting a compressor 380i :the proper capacity, the volume of auxiliary steam withdrawn from the flash chamber 30 is sufiicient to supply the heat required to raise the feed liquor temperature to the boiling point. The heating surface of heating element 12 is desirably made somewhat larger than in conventional recompression evaporators to provide'the heat exchange surface for carrying out this feed pre-heatin'g operation. However, the additional heatexchanger su'rface provided in heating element 12 is manifestly far less than the heating surface required in the counter-current exchangers previously 'used.

Turning now to Figures 24 of the-drawings,the recompression evaporator system there shown comprises an evaporator body 50 and heating element 52 that are generally similar to the body and element 12 of Figure 1 except that the heating-element and evaporator body are fabricated as a single unit. Vapors from the body 50 flow through a pipe 54 to a compressor 56 wherein they are compressed and delivered through a pipe 58 including-vapor drier 60 to thesteam' side "of the heating element 52.

In the evaporator 52 a multipass heating element is used to improve'the efliciency of evaporation. Referring to Figure 3, the lower'po'rtio'n of evaporator body 50 is divided vertically into four quadrants, '62, '64, '66 and 68 by the vertical partitions 70 and 72 that .intersect at right-angles and extend to the wall of evaporator body 50. As shown in Figure 4, the "bottom of heating-element 72 iscorrespondingly divided into four quadrants by the partitions 76 and 78. The top of eachquadrant isconnected to the bottom of the nextsuccessive quadrant by a'series of liquor transfer pipes. More specifically, the top of quadrant 62 is connected by a pipe '80 with the bottom of quadrant 64; the top of quadrant 64 is-connected by a pipe 82 with the bottom of quadrant 66; the top of quadrant 66 is connected by a pipe '84 with the bottom of quadrant 68; and the top of quadrant 68 is connected by a pipe-86 with the bottom of quadrant 62.- -Thus the liquor that flows from the top of the tubes of each quadrant of the heating element is recirculated downwardly to the bottomof the tubes of the next suc- 'cessive quadrant in a counter-clockwise direction. Feed liquor enters the system, and more particularly the bottom of quadrant62, through a pipe 88 and concentrated liquor leaves the system through a pipe90 which is connected to pipe 86. Pipe 90 contains a valve 91 and the lower portion of'pipe 86 contains a valve 93 .to'permit the flow of liquor through pipe 86 to be selectively directed either to the discharge pipe 90 or the lower end of quadrant 62 as disired.

As in the system of Figure 1, condensate flashis-used ;to provide auxiliary steam for pre-heating the feed liquor. Condensate is withdrawn from the steam side'of heating'element 52'through a pipe 92 and flows to theflash chamber 94 which, like'the flash chamber 30, is'Hprovided with a liquid level regulator '96 and condensate .4 discharge pipe 98. Flash vapor from the chamber 94 leaves the top of the chamber through a pipe and flows to a thermo-compressor 102 which in this case is a steam jet injector that is supplied with high pressure steam through a pipe 104. The thermo-compressor 102 compresses the flash vapor and delivers it through a pipe 106 to the pipe 54 wherein it mixes with the main body of vapor coming from the evaporator body 50. The mixed vapor is compressed by compressor 56 and delivered to the steam side of heating element 52. It is evident that the system of Figure 2, like that of 'Figure 1, eliminates the relatively costly countercurrent heat exchangers previously used in such recompression evaporation systems.

It will be evident from the foregoing discussion that the present invention provides a method and apparatus capable of achieving the several objects that are set forth at the beginning of the present specification. The costly counter-current heat exchangers previously used are eliminated .in the present system. Moreover, the condensate flash provides a convenient and adequate auxiliary source of steam for supplying the additional heat required to preheat the feed liquor. It is of course to be understood that the foregoing description is illustrative only and that numerous changes can be made in the apparatus described and its mode of operation without departing from the spirit of the invention as .defined in the appended claims.

I claim:

1, In a recompression evaporator of the type that in- .cludesan evaporator body adapted to contain a quantity of liquor to be evaporated, a heating element operatively associated with said evaporator body, said heating element having a liquor side through which the liquor to be evaporated flows to said evaporator body and a vapor side wherein vapor is condensed to supply heat to said liquor, and a vapor'compressor for compressing vapors evaporated from said liquor in said heating element .and evaporator body and supplying them to the vapor side of said heatingelement, the combination with said heating element, evaporator body and vapor compressor of a condensate flash chamber connected to the vaporside of said heating element to receive condensed vapor therefrom and auxiliary compressor means having an intake connected to said flash chamber whereby the .pressure in said flash chamber is lowered to cause at least a portion of the condensed vapor therein to be vaporized, the discharge of said auxiliary compressor means being effectively connected to the 'vapor side of said heating element.

2. A recompression evaporator according to claim 1 and wherein said auxiliary compressor means is a steam jet.

3. A recompression evaporator according to claim w1 and wherein said auxiliary compressor means is a mechanical compressor.

4. In a recompression evaporator of the type that includes an evaporator body, a tube-in-shell heating element 'opera'tively associated with said evaporator body,

the tubeso'f said heating element constituting the liquor side thereof through which the liquor to be evaporated flows to said evaporator body and the shell of said heating elem'ent constituting the vapor side thereof wherein a condensible vapor is condensed to supply heat to said liquor,'the liquor discharge end of said heating element being located .in said evaporator body, whereby heated liquor l'eaving said tubesflows into the bottom of said heating element evaporator body and vapor compressor .of acondensateflashcharnber connected to the vapor :side ofsaid heating element to receive condensedvapor therefrom, auxiliary compressor means having an intake connected to said flash chamber, whereby the pressure in said flash chamber is lowered to cause a portion of the condensed vapor therein to re-vaporize, the discharge of said auxiliary compressor means being effec tively connected to the vapor side of said heating element, partitions at the liquor inlet and liquor outlet ends of said heating element efiectively dividing the tubes thereof into separate sections, and conduits connecting the liquor discharge ends of each section with the inlet end of another section, whereby the liquor to be evaporated passes in series through the several sections of said heating element.

5. The method of evaporating a liquor in a recompression evaporator of the type that includes an evaporator body adapted to contain a quantity of liquor to be evaporated, a heating element operatively associated with said evaporator body, said heating element having a liquor side through which the liquor to be evaporated flows to said evaporator body and a vapor side wherein vapor is condensed to supply heat to said liquor, and a vapor compressor for compressing vapors evaporated from said liquor in said heating element and evaporator body and supplying them to the vapor side of said heating element, said method comprising the steps of supplying liquor to be evaporated to the liquor side of said heating element, compressing vapors evolved in said evaporator body and delivering them to the vapor side of said heating element, removing condensate from the vapor side of said heating element, reducing the pressure on said condensate to cause at least a portion thereof to flash into vapor, and compressing said flash vapor and delivering it to the vapor side of said heating element.

6. The method of evaporating a liquor in a recompression evaporator of the type that includes an evaporator body adapted to contain a quantity of liquor to be evaporated, a heating element operatively associated with said evaporator body, said heating element having a liquor side through which the liquor to be evaporated flows to said evaporator body and a vapor side wherein vapor is condensed to supply heat to said liquor, and a vapor compressor for compressing vapors evaporated from said liquor in said heating element and evaporator body and supplying them to the vapor side of said heating element, said method comprising the steps of supplying liquor to be evaporated to the liquor side of said heating element, compressing vapors evolved in said evaporator body and delivering them to the vapor side of said heating element, removing condensate from the vapor side of said heating element, reducing the pressure on said condensate to cause at least a portion thereof to flash into vapor, mixing said flash vapor with vapor evolved in said vapor body, and compressing the resulting vapor mixture and delivering it to the vapor side of said heating element.

7. In a recompression evaporator of the type that includes an evaporator body adapted to contain a quantity of liquor to be evaporated, a heating element operatively associated with said evaporator body, said heating element having a liquor side through which the liquor to be evaporated flows to said evaporator body and a vapor side wherein vapor is condensed to supply heat to said liquor, and a vapor compressor for compressing vapors evaporated from said liquor in said heating element and evaporator body and supplying them to the vapor side of said heating element, the combination with said heating element, evaporator body, and vapor compressor of a condensate flash chamber connected to the vapor side of said heating element to receive condensed vapor therefrom, and auxiliary compressor means having an intake connected to said flash chamber, whereby the pressure in said flash chamber is lowered to cause at least a portion of the condensate therein to be vaporized, the discharge of said auxiliary compressor means being connected to the intake of said vapor compressor.

8. A recompression evaporator according to claim 7 and wherein said auxiliary compressor means is a steam jet.

9. A recompression evaporator according to claim 7 and wherein said auxiliary compressor means is a mechanical compressor.

References Cited in the file of this patent UNITED STATES PATENTS 896,460 Prache et a1. Aug. 18, 1908 1,425,005 Gensecke Aug. 8, 1922 1,916,073 Rosenblad June 27, 1933 2,660,236 Farnsworth Nov. 24, 1953 2,707,022 Hesler Apr. 26, 1955 2,764,233 Skinner Sept. 25, 1956 FOREIGN PATENTS 114,838 Great Britain Sept. 4, 1919 556,686 France July 25, 1923 650,047 Germany Nov. 9, 1937 

